Reverse Osmosis water filter

 We have moved within the past year to an area that has extermely hard
water.  My wife does not like the taste of it or the feel even though I
have installed a water softener.  We received a mail solicitation from
a local water products company for an under sink reverse osmosis water
filter system installed for $425.

The company has a good reputation and over 40 years in business with
minor to none BBS complaints.

I don't know if this is a good price or not.  For those who have
installed one, is this a good price.  What should I expect for ongoing
maintenance supplies (mot price, but what), if any ?

Thanks for any and all replies.